The world’s oceans are in a “shocking” state and marine species may face an unprecedented extinction event, an international panel of experts has warned.

The many threats to the world’s coral reefs include increasing ocean temperatures, which can cause coral ‘bleaching’, as shown in this Acropora species.

The panel was brought together by the International Programme on the State of the Ocean (IPSO) and involved scientists from across a range disciplines. It was the first to consider the cumulative impacts of the pressures facing the oceans, including pollution, ocean acidification, ocean warming, over-fishing and hypoxia (reduced oxygen levels).

Rapid pace of change

“The findings are shocking,” said Alex Rogers, Scientific Director of IPSO and a professor of conservation biology at Oxford University. “As we considered the cumulative effect of what humankind does to the oceans, the implications became far worse than we had individually realised… almost right across the board we’re seeing changes that are happening faster than we’d thought, or in ways that we didn’t expect to see for hundreds of years.”

Overfishing has brought species such as the southern bluefin tuna to the brink of extinction.

These rapid changes include the melting of the Greenland and Antarctic ice sheets, sea level rise, and the release of methane trapped in the sea bed. More worrying is how different threats are acting together in ways that had not previously been recognised, their combined effects being worse than each threat alone.

For example, some pollutants have been found to stick to the surfaces of tiny plastic particles in the ocean, increasing the amounts of these pollutants being consumed by marine creatures. Global climate change, ocean acidification, pollution and overfishing are also working together to increase the pressures on the world’s coral reefs, many of which are now in severe decline.

Coral reefs support a huge variety of other species, including fish such as these common clownfish.

Sixth mass extinction?

The combined effects of these stresses mean that ocean ecosystems are unable to recover, being constantly under attack from multiple threats. The panel concluded that not only are we already seeing significant declines in marine species and habitats, but that we now face losing species and entire marine ecosystems, such as coral reefs, within a single generation.

Life on Earth has gone through five “mass extinction” events in the past, and human activities are now thought to be causing a sixth such event. The panel’s report said that the combination of threats to the ocean is creating the same conditions found in every major extinction in Earth’s history. Levels of carbon dioxide being absorbed by the ocean are already far greater than at the time of the last mass extinction of marine life, some 55 million years ago. The rate of the ocean’s degeneration is also far greater than anyone had predicted.

Manta ray entangled in a fishing net.

Conserving the world’s oceans

The panel’s conclusions will be presented in a report at the UN headquarters in New York later this week, when discussions will take place aimed at reforming governance of the oceans. The report calls for urgent measures to better conserve ocean ecosystems, and in particular to improve governance of the largely unprotected high seas.

IPSO’s immediate recommendations include stopping exploitative fishing, especially on the high seas where there is little effective regulation. It also recommends mapping and then reducing pollutants, such as plastics, fertilisers and human waste, which are entering the oceans. In addition, sharp reductions need to be made in greenhouse gas emissions, and research is urgently needed into ways of reducing carbon dioxide in the atmosphere.

Like many marine species, the green turtle faces a range of threats. This species is classified as Endangered by the IUCN.

One of the report’s co-authors, Dan Laffoley, Marine Chair of IUCN’s World Commission on Protected Areas, and Senior Advisor on Marine Science and Conservation for IUCN, admitted that the challenges were vast. “But unlike previous generations, we know what now needs to happen,” he said. “The time to protect the blue heart of our planet is now.”